The service's methadone programme is undertaking an internal review, partly to examine ways of reducing the number of people in the Cads-based programme.
Contracted for 235 people, Cads was directly treating 290, while GP administered methadone, which should have 85 users, had 50.
Otago lagged behind other major centres in moving people on to GP-managed programmes.
About 20 people were on the waiting list for the Cads programme, receiving a fixed amount of methadone in the meantime.
This programme was not tailored to meet individual need.
Cads was "stretched" at present, Dr Cape said.
Encouraging the move to GPs was not about saving money, but reducing the burden on staff.
Dr Cape said 24 GPs in Otago were registered to administer methadone.
"Some GPs are very very good. Some will absolutely refuse, for some unknown reason, to have drug addicts in their clinic."
Only people who were "safe and stable" were put on the GP methadone programme, he said.
He acknowledged the cost for methadone users was potentially higher, as they had to pay for GP appointments, although help was available from social agencies.
Those seeing a GP for methadone could still receive counselling from Cads, if necessary.
Dr Cape said he used his lecturing role with University of Otago medical students to promote the methadone programme.
Education was key, he said.
"It would be good if more people show more willingness to show an interest in addiction as a health problem."
Dr Cape hoped drug funder Pharmac would subsidise methadone alternative buprenorphine, which suited some people better.
About 20 people in the past 18 months had self-funded buprenorphine, which cost about $200 a month.
It was commonly used overseas, as some people found it easier to wean themselves off than methadone.
A spokesman for Pharmac said the agency was "continuing to look for ways in which [Buprenorphine] could be funded. However, we don't have a timeframe for when anything might happen".
Specialist mental health service manager Steve Bayne said a focus of the review was also to prepare for the shift to Wakari Hospital, from rented premises in Moray Pl, expected to be towards the end of next month.
